This invention relates to a cam plate type axial piston pump adapted to control an inclination rotation angle of a cam plate to control discharge from the pump, and more particularly to a cam plate type axial piston pump which is optimum for use for a hydrostatic power transmission.
A conventional cam plate type axial piston pump of such type is typically constructed in such a manner that when it is used for a hydrostatic power transmission, control of its forward movement, backward movement and stoppage is generally carried out by varying an inclination angle of a cam plate of the pump. More particularly, the cam plate type axial piston pump is adapted to exhibit its stoppage function when a control lever is held at a neutral position to keep an inclination angle of the cam plate zero, and its forward movement or backward movement function is carried out by inclining the cam plate from the zero degree position in a desired direction. This results in movement or stoppage of a driven unit such as a vehicle or the like taking place through the hydrostatic power transmission. Thus, the conventional cam plate type axial piston pump fails to exhibit its satisfactory stoppage function, unless an inclination angle of the cam plate is positively rendered zero when the control lever is held at the neutral position.
Unfortunately, when the control lever is provided with only one stop point or position for the purpose of stoppage of the driven unit, any external force such as mechanical vibration or the like which is applied to the control lever causes the stop point to deviate. In particular, this causes insufficient operation, for example, by an unskilled operator, to fail to positively set the control lever at the stop point, resulting in safety of the driven unit being highly deteriorated.
In view of the foregoing, a cam plate type axial piston pump was proposed which is provided with a mechanism connected to the driven unit and adapted to exhibit unsteadiness when a control lever is positioned adjacent to its neutral position.
In general, it is known that a cam plate type axial piston pump, when it reaches a position near its neutral point, exhibits self-return function which causes it to further return to the neutral point. The proposed cam plate type axial piston pump, as described above, is so constructed that the connection mechanism may exhibit unsteadiness when the control lever is positioned adjacent to the neutral position.
Neutral characteristics of the proposed cam plate type axial piston pump constructed as described above depend on unsteadiness of the pump and unsteadiness is varied depending on the individual piston pump. Accordingly, neutral point return characteristics of the pump are varied on the individual piston pump.
Further, the proposed pump has another disadvantage that the control lever and/or a cam plate are apt to vibrate due to wear or deformation of the connection mechanism, resulting in a variation of its neutral point return characteristics. The neutral point return characteristics are also varied due to a failure in control of an inclination angle of the cam plate with high accuracy.